Sensory, local and general autonomic, and affective reactions, associated with TMD myalgia are of great importance to many patients. These symptoms are poorly understood as far as deep nociception is concerned, and even less is known about the spatial and temporal sequence with which they occur in response to pain, or relative to each other. Differential diagnosis continues to be a challenge because sensory, affective and autonomic symptoms and signs can be troublesome. With care providers being puzzled about the reported symptoms, it is not surprising that some patients with complex symptoms express the feeling of not being understood. This application will focus on experimental unilateral masticatory myalgia, testing hypotheses concerning the significance of masticatory myalgia to sensory and autonomic function over painful and nonpainful facial sites on ipsilateral and contralateral sides relative to pain. In addition, studies are proposed to examine how sensory, autonomic and affective functions change with time in the presence of deep pain. With pain being induced by the infusion of an algesic substance, alternatives to the null hypotheses, that the infusion of either the algesic or the control substance causes a change in sensory, affective and autonomic function relative to baseline, will be studied. Specifically, studies are proposed to determine whether masticatory myalgia influences the low-threshold mechanosensitivity of the facial skin, or the pressure-pain threshold of facial tissues. By inducing and maintaining pain, whether muscle pain is causing changes in sudomotor function, breathing, and mood will also be studied. Finally, whether masticatory myalgia, induced in masseteric and temporal sites causes specific spatial pain distributions, will be assessed. The proposed studies are expected to increase current understanding of whether muscle pain is causing some of the symptoms associated with TMD myalgia, for which there is currently no good explanation.